The present invention concerns an impeller for a pump, especially a vortex pump, the said impeller being provided with one or more straight or curved vanes arranged radially.
For the purpose of pumping sewage, the vortex pump has proved to be the most advantageous type of pump in respect of proneness to blockages, durability, running stability and production costs. Furthermore, the vortex pump is well adapted for pumping silt and pulp as well as for applications involving heavy wear, e.g. for use in places where sand can enter the pump. A typical feature of a vortex pump is that it has between the impeller and the pump housing a wide space without vanes, the width of the space corresponding to the flow capacity of the pump. Moreover, the impeller vanes used in vortex pumps are not provided with front edges transverse to the flow passage, on which solid substances of long fibrelike structure could be entagled. However, a drawback with prior-art vortex pumps is a low efficiency and a low lift curve. This is due to the fact that a detrimental flow takes place over the edges of the impeller vanes, which is again due to the difference of pressure above and below the vanes.